The present invention relates generally to a suspension control system for an automotive vehicle for controlling damping characteristics or stiffness of a vehicular suspension system depending upon vehicle driving conditions. In particular, the invention relates to an automotive suspension control system which performs anti-dive control for suppressing nose-dive and rebounding after nose-dive during deceleration of the vehicle.
Published Japanese Utility Model Application (Jikkai) Sho. No. 56-111009, discloses a suspension system having a variable shock absorber with adjustable shock-absorbing characteristics. The shock absorber is associated with a controller which controls its damping force. The controller operates the shock absorber so as to produce a higher damping force when it detects deceleration of the vehicle. The higher damping force is maintained as long as the vehicle brakes are applied to decelerate the vehicle. In other words, as soon as the brakes are released, the damping force to be produced by the shock absorber is reduced.
When applying brakes in order to stop the vehicle, the center of gravity shifts forward due to the inertia of the vehicle, which causes to the vehicle "nose dive". By adjusting the damping force to be produced by the shock absorber to HIGH, the magnitude of nose dive can be limited. On the other hand, at the end of vehicle deceleration, the center of gravity moves rearward, causing the front end of the vehicle to rebound. In particular, when the brake is released immediately after the vehicle stops, the controller orders the shock absorber to lower its damping force. This may intensify the rebounding behavior of the vehicle and degrade riding comfort.
Another approach has been discussed in the Published Japanese Patent Application (Tokkai) Showa 58-30816, in which abrupt deceleration of the vehicle is detected by means of a pressure sensor disposed within a hydraulic brake circuit. When abrupt deceleration of the vehicle is indicated by the pressure sensor signal value, the suspension system is hardened in order to suppress nose-dive. This suspension control technique may succeed in preventing nose-dive of the vehicle. However, since the magnitude of nose-dive varies with the deceleration of the vehicle, and rebounding magnitude after nose-dive varies with the magnitude of the nose-dive, the aforementioned suspension control system does not provide satisfactorily precise control of the suspension stiffness or damping characteristics according to the vehicle driving conditions.